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1.
The short-term effects of excessive NH4+-N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH4+ concentration, an excess of NH4+-N does not further increase NO3− formation rate in the soil, but only supports accumulation of NO2−-N and gaseous losses of N as N2O. Soils were amended with 10 to 500 μg NH4+-N g−1 soil. In both soils, addition of NH4+-N increased production of NO3−-N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N2O increased in the whole range of amendments in both soils. At the highest level of NH4+-N addition, NO2−-N accumulated in cattle-affected soil while NO3−-N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH4+-N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N2O.  相似文献   

2.

Purpose  

Vegetable production is one of the most intensive agricultural systems with high rates of nitrogen (N) fertilizer use and irrigation, conditions conducive for nitrate (NO3−) leaching, and nitrous oxide (N2O) emissions. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3− leaching and N2O emissions in vegetable production systems.  相似文献   

3.

Purpose  

Methanotrophs are an important group of methane (CH4)-oxidizing bacteria in the soil, which act as a major sink for the greenhouse gas, CH4. In grazed grassland, one of the ecologically most sensitive areas is the animal urine patch soil, which is a major source of both nitrate (NO3 −) leaching and nitrous oxide (N2O) emissions. Nitrification inhibitors, such as dicyandiamide (DCD), have been used to mitigate NO3 − leaching and N2O emissions in grazed pastures. However, it is not clear if the high nitrogen loading rate in the animal urine patch soil and the use of nitrification inhibitors would have an impact on the abundance of methanotrophs in grazed grassland soils. The purpose of this study was to determine the effect of animal urine and DCD on methanotroph abundance in grazed grassland soils.  相似文献   

4.
The effect of reduced tillage (RT) on nitrous oxide (N2O) emissions of soils from fields with root crops under a temperate climate was studied. Three silt loam fields under RT agriculture were compared with their respective conventional tillage (CT) field with comparable crop rotation and manure application. Undisturbed soil samples taken in September 2005 and February 2006 were incubated under laboratory conditions for 10 days. The N2O emission of soils taken in September 2005 varied from 50 to 1,095 μg N kg−1 dry soil. The N2O emissions of soils from the RT fields taken in September 2005 were statistically (P < 0.05) higher or comparable than the N2O emissions from their respective CT soil. The N2O emission of soils taken in February 2006 varied from 0 to 233 μg N kg−1 dry soil. The N2O emissions of soils from the RT fields taken in February 2006 tended to be higher than the N2O emissions from their respective CT soil. A positive and significant Pearson correlation of the N2O–N emissions with nitrate nitrogen (NO3 −–N) content in the soil was found (P < 0.01). Leaving the straw on the field, a typical feature of RT, decreased NO3 −–N content of the soil and reduced N2O emissions from RT soils.  相似文献   

5.
Crop residues with high C/N ratio immobilize N released during decomposition in soil, thus reducing N losses through leaching, denitrification, and nitrous oxide (N2O) emission. A laboratory incubation experiment was conducted for 84 days under controlled conditions (24°C and moisture content 55% of water-holding capacity) to study the influence of sugarcane, maize, sorghum, cotton and lucerne residues, and mineral N addition, on N mineralization–immobilization and N2O emission. Residues were added at the rate of 3 t C ha−1 to soil with, and without, 150 kg urea N ha−1. The addition of sugarcane, maize, and sorghum residues without N fertilizer resulted in a significant immobilization of soil N. Amended soil had significantly (P < 0.05) lower NO3−–N, which reached minimum values of 2.8 mg N kg−1 for sugarcane (at day 28), 10.3 mg N kg−1 for maize (day 7), and 5.9 mg N kg−1 for sorghum (day 7), compared to 22.7 mg N kg−1 for the unamended soil (day 7). During 84 days of incubation, the total mineral N in the residues + N treatments were decreased by 45 mg N kg−1 in sugarcane, 34 mg kg−1 in maize, 29 mg kg−1 in sorghum, and 16 mg kg−1 in cotton amended soil compared to soil + N fertilizer, although soil NO3−–N increased by 7 mg kg−1 in lucerne amended soil. The addition of residues also significantly increased amended soil microbial biomass C and N. Maximum emissions of N2O from crop residue amended soils occurred in the first 4–5 days of incubation. Overall, after 84 days of incubation, the cumulative N2O emission was 25% lower with cotton + N fertilizer, compared to soil + N fertilizer. The cumulative N2O emission was significantly and positively correlated with NO3−–N (r = 0.92, P < 0.01) and total mineral N (r = 0.93, P < 0.01) after 84 days of incubation, and had a weak but significant positive correlation with cumulative CO2 in the first 3 and 5 days of incubation (r = 0.59, P < 0.05).  相似文献   

6.
Nitrous oxide (N2O) emissions, soil microbial community structure, bulk density, total pore volume, total C and N, aggregate mean weight diameter and stability index were determined in arable soils under three different types of tillage: reduced tillage (RT), no tillage (NT) and conventional tillage (CT). Thirty intact soil cores, each in a 25 × 25-m2 grid, were collected to a depth of 10 cm at the seedling stage of winter wheat in February 2008 from Maulde (50°3′ N, 3°43′ W), Belgium. Two additional soil samples adjacent to each soil core were taken to measure the spatial variance in biotic and physicochemical conditions. The microbial community structure was evaluated by means of phospholipid fatty acids analysis. Soil cores were amended with 15 kg NO3−-N ha−1, 15 kg NH4+-N ha−1 and 30 kg ha−1 urea-N ha−1 and then brought to 65% water-filled pore space and incubated for 21 days at 15°C, with regular monitoring of N2O emissions. The N2O fluxes showed a log-normal distribution with mean coefficients of variance (CV) of 122%, 78% and 90% in RT, NT and CT, respectively, indicating a high spatial variation. However, this variability of N2O emissions did not show plot scale spatial dependence. The N2O emissions from RT were higher (p < 0.01) than from CT and NT. Multivariate analysis of soil properties showed that PC1 of principal component analysis had highest loadings for aggregate mean weight diameter, total C and fungi/bacteria ratio. Stepwise multiple regression based on soil properties explained 72% (p < 0.01) of the variance of N2O emissions. Spatial distributions of soil properties controlling N2O emissions were different in three different tillages with CV ranked as RT > CT > NT.  相似文献   

7.
In the tropics,frequent nitrogen(N)fertilization of grazing areas can potentially increase nitrous oxide(N2O)emissions.The application of nitrification inhibitors has been reported as an effective management practice for potentially reducing N loss from the soil-plant system and improving N use efficiency(NUE).The aim of this study was to determine the effect of the co-application of nitrapyrin(a nitrification inhibitor,NI)and urea in a tropical Andosol on the behavior of N and the emissions of N2O from autotrophic and heterotrophic nitrification.A greenhouse experiment was performed using a soil(pH 5.9,organic matter content 78 g kg-1,and N 5.6 g kg-1)sown with Cynodon nlemfuensis at 60%water-filled pore space to quantify total N2O emissions,N2O derived from fertilizer,soil ammonium(NH4+)and nitrate(NO3-),and NUE.The study included treatments that received deionized water only(control,NI).No significant differences were observed in soil NH4+content between the UR and UR+NI treatments,probably because of soil mineralization and NO3-produced by heterotrophic nitrification,which is not effectively inhibited by nitrapyrin.After 56 d,N2O emissions in UR(0.51±0.12 mg N2O-N concluded that the soil organic N mineralization and heterotrophic nitrification are the main processes of NH4+and NO3-production.Additionally,it was found that N2O emissions were partially a consequence of the direct oxidation of the soil's organic N via heterotrophic nitrification coupled to denitrification.Finally,the results suggest that nitrapyrin would likely exert significant mitigation on N2O emissions only if a substantial N surplus exists in soils with high organic matter content.  相似文献   

8.
Application of feedlot manure (FLM) to cropping and grazing soils could provide a valuable N nutrient resource. However, because of its high but variable N concentration, FLM has the potential for environmental pollution of water bodies and N2O emission to the atmosphere. As a potential management tool, we utilised the low-nutrient green waste compost (GWC) to assess its effectiveness in regulating N release and the amount of N2O emission from two Vertisols when both FLM and GWC were applied together. Cumulative soil N2O emission over 32 weeks at 24°C and field capacity (70% water-filled pore space) for a black Vertisol (Udic Paleustert) was 45 mg N2O m−2 from unamended soil. This increased to 274 mg N2O m−2 when FLM was applied at 1 kg m−2 and to 403 mg N2O m−2 at 2 kg m−2. In contrast, the emissions of 60 mg N2O m−2 when the soil was amended with GWC 1 kg m−2 and 48 mg N2O m−2 at 2 kg m−2 were not significantly greater than the unamended soil. Emission from a mixture of FLM and GWC applied in equal amounts (0.5 kg m−2) was 106 mg N2O m−2 and FLM applied at 0.5 kg m−2 and GWC at 1.5 kg GWC m−2 was 117 mg N2O m−2. Although cumulative N2O emissions from an unamended grey Vertisol (Typic Chromustert) were only slightly higher than black Vertisol (57 mg N2O m−2), FLM application at 1 kg m−2 increased N2O emissions by 14 times (792 mg N2O m−2) and at 2 kg m−2 application by 22 times (1260 mg N2O m-2). Application of GWC did not significantly increase N2O emission (99 mg N2O m−2 at 1 kg m−2 and 65 mg N2O m−2 at 2 kg m−2) above the unamended soil. As observed for the black Vertisol, a mixture of FLM (0.5 kg m−2) and GWC (0.5 or 1.5 kg m−2) reduced N2O emission by >50% of that from the FLM alone, most likely by reducing the amount of mineral N (NH4+–N and NO3−–N) in the soil, as mineral N in soil and the N2O emission were closely correlated.  相似文献   

9.
The following six pig slurries obtained after acidification and/or solid/liquid separation were used in the research: original (S) and acidified (AS) pig slurry, nonacidified (LF) and acidified (ALF) pig slurry liquid fraction, and nonacidified (SF) and acidified (ASF) pig slurry solid fraction. Laboratory incubations were performed to assess the effect of the application of these slurries on N mineralization and CO2 and N2O emissions from a sandy soil. Acidification maintained higher NH4 +-N contents in soil particularly in the ALF-treated soil where NH4 +-N contents were two times higher than in LF-treated soil during the 55–171-day interval. At the end of the incubation (171 days), 32.9 and 24.2 mg N kg−1 dry soil were mineralized in the ASF- and SF-treated soils, respectively, but no mineralization occurred in LF- and S-treated soils, although acidification decreased N immobilization in ALF- (−25.3 mg N kg−1 soil) and AS- (−12.7 mg N kg−1 soil) compared to LF- (−34.4 mg N kg−1 soil) and S-treated (−18.6 mg N kg−1 soil) soils, respectively. Most of the dissolved CO2 was lost during the acidification process. More than 90% of the applied C in the LF-treated soil was lost during the incubation, indicating a high availability of the added organic compounds. Nitrous oxide emissions occurred only after day 12 and at a lower rate in soils treated with acidified than nonacidified slurries. However, during the first 61 days of incubation, 1,157 μg N kg−1 soil was lost as N2O in the AS-treated soil and only 937 in the S-treated soil.  相似文献   

10.
 The spatial in situ variability of soil N2O emissions (measured by micro-chambers, radius 0.033 m), N2O content, water content, NO3 –, NH4 +, inorganic carbon and organic carbon concentrations was investigated on a silt loam by means of geostatistical methods and nonparametric statistics. The sampling grid consisted of different spacings between sampling points which ranged from 0.1 m to 50 m. There were no significant correlations between N2O emissions and soil parameters (P>0.1) when all the sampling points were considered. In the centre of the grid a "hot area" was localized with significantly higher N2O emissions, and NO3 – and NH4 + concentrations (P≤0.05). Within this hot area the N2O soil content significantly correlated with N2O emissions (P≤0.05). When semiovariograms were computed without data of the hot area samples, N2O emissions showed a weak spatial correlation (range: 4.3 m). The calculations including all data led to pure nugget effects for all parameters except for soil water content (range >40 m) and N2O soil content (range 16.4 m). Received: 19 December 1997  相似文献   

11.
A lysimeter experiment was carried out to evaluate the effects of the NH3 volatilization mitigation by adding anaerobically digested cattle slurry (ADCS) alone, with wood vinegar (WV) or with a higher level of floodwater (HFW), on emissions of CH4 and N2O from a paddy soil planted with fodder rice. We have carried out the following treatments: (1) chemical fertilizer, (2) ADCS, (3) ADCS + WV, and (4) ADCS + HFW; the height of floodwater was 10 cm in the latter treatment, and it was 3 to 4 cm in the other treatments just before fertilizer applications. Nitrogen fertilizer rate added to soil in each treatment was 30 g NH4+–N m−2 (split in one basal and two top-dressing additions). Ammonia volatilization in the ADCS treatment was 2.7 g NH3–N m−2 throughout the growing season, and it was significantly reduced by 79% and 55% in the ADCS + WV and ADCS + HFW treatments, respectively. The total amount of CH4 emitted in the ADCS treatment in the growing season was not significantly enhanced by the mitigation of NH3 volatilization either by adding wood vinegar or by increasing the height of the floodwater. Negligible N2O emissions were observed in all treatments during the growing period.  相似文献   

12.
 N2O emissions were periodically measured using the static chamber method over a 1-year period in a cultivated field subjected to different agricultural practices including the type of N fertilizer (NH4NO3, (NH4)2SO4, CO(NH2)2 or KNO3 and the type of crop (rapeseed and winter wheat). N2O emissions exhibited the same seasonal pattern whatever the treatment, with emissions between 1.5 and 15 g N ha–1 day–1 during the autumn, 16–56 g N ha–1 day–1 in winter after a lengthy period of freezing, 0.5–70 g N ha–1 day–1 during the spring and lower emissions during the summer. The type of crop had little impact on the level of N2O emission. These emissions were a little higher under wheat during the autumn in relation to an higher soil NO3 – content, but the level of emissions was similar over a 7-month period (2163 and 2093 g N ha–1 for rape and wheat, respectively). The form of N fertilizer affected N2O emissions during the month following fertilizer application, with higher emissions in the case of NH4NO3 and (NH4)2SO4, and a different temporal pattern of emissions after CO(NH2)2 application. The proportion of applied N lost as N2O varied from 0.42% to 0.55% with the form of N applied, suggesting that controlling this agricultural factor would not be an efficient way of limiting N2O emissions under certain climatic and pedological situations. Received: 1 December 1997  相似文献   

13.
Incubation of soil under low partial pressures of acetylene (10 Pa) is a widely used method to specifically inhibit nitrification due to the suicide inhibition of ammonium monooxygenase (AMO), the first enzyme in NH4 + oxidation by nitrifying bacteria. Although the inhibition of AMO is irreversible, recovery of activity is possible if new enzyme is synthesized. In experiments with three different soils, NH4 + concentrations decreased and NO3 – concentrations increased soon after acetylene was removed from the atmosphere. Recovery of NO production started immediately after the removal of acetylene. The release rates of NO and N2O were higher in soil samples which were only preincubated with 10 Pa acetylene than in those which were kept in the presence of 10 Pa acetylene. In the permanent presence of 10 Pa acetylene, NH4 + and NO3 – concentrations stayed constant, and the release rates of NO and N2O were low. These low release rates were apparently due to processes other than nitrification. Our experiments showed that the blockage of nitrification by low (10 Pa) acetylene partial pressures is only reliable when the soil is kept in permanent contact with acetylene. Received: 17 July 1996  相似文献   

14.
黏土中施加生物炭可改变土体的孔隙结构。生物炭掺量和干密度均会对土体的渗透系数产生影响,准确确定生物炭-黏土混合土的渗透系数对满足填埋场上覆层的功能需求就显得格外重要。采用自主研发设计的柔性壁水-气联合渗透测试装置,测定不同生物炭掺量和干密度的生物炭-黏土混合土的饱和渗透系数和渗气系数,得到生物炭掺量、干密度与渗气系数和渗水系数间的关系曲线。建立生物炭掺量和干密度双变化条件下的渗气渗水函数,并通过验证组验证该函数的适用性。研究结果表明：在干密度较小时,对比纯黏土的渗水率,添加5%、10%、15%和20%生物炭处理后的土样渗水系数kw值分别为8.25×10-17、8.89×10-17、10.40×10-17和18.25×10-17 m2,掺20%生物炭土样的渗透率增加了将近一个数量级。渗气渗水函数基于易测定的渗气率作为自变量,同时又考虑了干密度和生物炭掺量的影响,能快速、准确地确定土样的渗水系数。结合验证组试验得出,利用该函数计算得到的渗水系数和试验实测值吻合程度较好,表明该函数具有一定的适用性。本研究结果可为快速、准确确定渗水系数,定量描述非饱和土孔隙中水气运动之间的相互影响提供理论支撑。  相似文献   

15.
The objective of this study was to examine the effects of soil moisture, irrigation pattern, and temperature on gaseous and leaching losses of carbon (C) and nitrogen (N) from soils amended with biogas slurry (BS). Undisturbed soil cores were amended with BS (33 kg N ha−1) and incubated at 13.5°C and 23.5°C under continuous irrigation (2 mm day−1) or cycles of strong irrigation and partial drying (every 6 weeks, 1 week with 12 mm day−1). During the 6 weeks after BS application, on average, 30% and 3.8% of the C and N applied with BS were emitted as carbon dioxide (CO2) and nitrous oxide (N2O), respectively. Across all treatments, a temperature increase of 10°C increased N2O and CO2 emissions by a factor of 3.7 and 1.7, respectively. The irrigation pattern strongly affected the temporal production of CO2 and N2O but had no significant effect on the cumulative production. Nitrogen was predominantly lost in the form of nitrate (NO3−). On average, 16% of the N applied was lost as NO3−. Nitrate leaching was significantly increased at the higher temperature (P < 0.01), while the irrigation pattern had no effect (P = 0.63). Our results show that the C and N turnovers were strongly affected by BS application and soil temperature whereas irrigation pattern had only minor effects. A considerable proportion of the C and N in BS were readily available for soil microorganisms.  相似文献   

16.
 Nitrous oxide (N2O) emissions were measured from an irrigated sandy-clay loam cropped to maize and wheat, each receiving urea at 100 kg N ha–1. During the maize season (24 August–26 October), N2O emissions ranged between –0.94 and 1.53 g N ha–1 h–1 with peaks during different irrigation cycles (four) ranging between 0.08 and 1.53 g N ha–1 h–1. N2O sink activity during the maize season was recorded on 10 of the 29 sampling occasions and ranged between 0.18 and 0.94 g N ha–1 h–1. N2O emissions during the wheat season (22 November–20 April) varied between –0.85 and 3.27 g N ha–1 h–1, whereas peaks during different irrigation cycles (six) were in the range of 0.05–3.27 g N ha–1 h–1. N2O sink activity was recorded on 14 of the 41 samplings during the wheat season and ranged between 0.01 and 0.87 g N ha–1 h–1. Total N2O emissions were 0.16 and 0.49 kg N ha–1, whereas the total N2O sink activity was 0.04 and 0.06 kg N ha–1 during the maize and wheat seasons, respectively. N2O emissions under maize were significantly correlated with denitrification rate and soil NO3 –-N but not with soil NH4 +-N or soil temperature. Under wheat, however, N2O emissions showed a strong correlation with soil NH4 +-N, soil NO3 –-N and soil temperature but not with the denitrification rate. Under either crop, N2O emissions did not show a significant relationship with water-filled pore space or soil respiration. Received: 11 June 1997  相似文献   

17.
Abstract

Two experiments were conducted to evaluate the inhibitory effects of 2-chloro-6 (trichloromethyl) pyridine (nitrapyrin) and dicyandiamide on nitrous oxide (N2O), a greenhouse gas, emission from soils amended with ammonium sulfate. In the two experiments, samples of an Andosol and a Gray Lowland soil were kept in glass vessels sealed with a butyl rubber cap and incubated at 25°C. In the first experiment, nitrapyrin (1 µg g?1 dry soil) and dicyandiamide (10 µg g?1 dry soil) were applied to samples of a water-saturated Andosol and a Gray Lowland soil to which ammonium sulfate had been applied at a rate of 0.1 mg N g?1 dry soil. Nitrapyrin decreased N2O emissions from the Andosol and the Gray Lowland soil by 71% and 24%, respectively. Dicyandiamide decreased N2O emissions from the Andosol and Gray Lowland soil by 31% and 18%, respectively. In the second experiment, nitrapyrin (1 µg g?1 dry soil) was applied to samples of an Andosol at 51% water-filled pore space to which ammonium sulfate had been applied at rates of 0.01, 0.1 and 0.5 mg N g?1 dry soil. Nitrapyrin decreased N2O emissions by 62%, 83% and 74%, respectively. Changes in the NH+ 4 and NO? 2 + NO? 3 concentrations in soil showed that nitrapyrin and dicyandiamide slowed down the nitrification process, but did not completely stop the process at any time. The results reveal the potential of nitrification inhibitors to decrease N2O emission from fertilized soil in a wide range of moisture conditions and nitrogen levels.  相似文献   

18.
In this study, we investigated N2O emissions from two fields under minimum tillage, cropped with maize (MT maize) and summer oats (MT oats), and a conventionally tilled field cropped with maize (CT maize). Nitrous oxide losses from the MT maize and MT oats fields (5.27 and 3.64 kg N2O-N ha−1, respectively) were significantly higher than those from the CT maize field (0.27 kg N2O-N ha−1) over a period of 1 year. The lower moisture content in CT maize (43% water-filled pore space [WFPS] compared to 60–65%) probably caused the difference in total N2O emissions. Denitrification was found to be the major source of N2O loss. Emission factors calculated from the MT field data were high (0.04) compared to the CT field (0.001). All data were simulated with the denitrification decomposition model (DNDC). For the CT field, N2O and N2O + N2 emissions were largely overestimated. For the MT fields, there was a better agreement with the total N2O and N2O + N2 emissions, although the N2O emissions from the MT maize field were underestimated. The simulated N2O emissions were particularly influenced by fertilization, but several other measured N2O emission peaks associated with other management practices at higher WFPS were not captured by the model. Several mismatches between simulated and measured \textNH4+ {\text{NH}}_4^ + , \textNO3- {\text{NO}}_3^ - and WFPS for all fields were observed. These mismatches together with the insensitivity of the DNDC model for increased N2O emissions at the management practices different from fertilizer application explain the limited similarity between the simulated and measured N2O emissions pattern from the MT fields.  相似文献   

19.
Nitrous oxide (N2O) from agricultural soil is a significant source of greenhouse gas emissions. Biochar amendment can contribute to climate change mitigation by suppressing emissions of N2O from soil, although the mechanisms underlying this effect are poorly understood. We investigated the effect of biochar on soil N2O emissions and N cycling processes by quantifying soil N immobilisation, denitrification, nitrification and mineralisation rates using 15N pool dilution techniques and the FLUAZ numerical calculation model. We then examined whether biochar amendment affected N2O emissions and the availability and transformations of N in soils.Our results show that biochar suppressed cumulative soil N2O production by 91% in near-saturated, fertilised soils. Cumulative denitrification was reduced by 37%, which accounted for 85–95 % of soil N2O emissions. We also found that physical/chemical and biological ammonium (NH4+) immobilisation increased with biochar amendment but that nitrate (NO3−) immobilisation decreased. We concluded that this immobilisation was insignificant compared to total soil inorganic N content. In contrast, soil N mineralisation significantly increased by 269% and nitrification by 34% in biochar-amended soil.These findings demonstrate that biochar amendment did not limit inorganic N availability to nitrifiers and denitrifiers, therefore limitations in soil NH4+ and NO3− supply cannot explain the suppression of N2O emissions. These results support the concept that biochar application to soil could significantly mitigate agricultural N2O emissions through altering N transformations, and underpin efforts to develop climate-friendly agricultural management techniques.  相似文献   

20.
Previous studies have demonstrated inconsistent results on the impact of tillage systems on nitrogen (N) losses from field-applied manure. This study assessed the impact of no-tillage (NT) and conventional tillage (CT) systems on gaseous N losses, N2O:N2O + N2 ratios and NO3−-N leaching following surface application of cattle manure. The study was undertaken during the 2003/2004 and 2004/2005 seasons at two field sites in Nova Scotia namely, Streets Ridge (SR) in Cumberland County and the Bio-environmental Engineering Centre (BEEC) in Truro. Results showed that the NT system had higher (p < 0.05) NH3 losses than CT. Over the two seasons, manure incorporation in CT reduced NH3 losses on average by 86% at SR and 78% at BEEC relative to NT. At both sites and during both seasons, denitrification rates and N2O fluxes in NT were generally higher than in CT plots, presumably due to higher soil water and organic matter content in NT. Over the two seasons, mean denitrification rates at SR were 239 and 119 g N ha−1 d−1, while N2O fluxes were 120 and 64 g N ha−1 d−1 under NT and CT, respectively. At BEEC mean denitrification rates were 114 and 71 g N ha−1 d−1, while N2O fluxes were 52 and 27 g N ha−1 d−1 under NT and CT, respectively. Conversely, N2O:N2O + N2 ratios were lower in NT than CT suggesting more complete reduction of N2O to N2 under NT. When averaged across all soil depths, NO3−-N was higher (p < 0.05) in CT than NT. Nitrate-N decreased with depth at both sites regardless of tillage. In most cases, NO3−-N was higher under CT than NT at all soil depths. Similarly, flow-weighted average NO3−-N concentrations in drainage water were generally higher under CT. This may be partly attributed to higher denitrification rates under NT. Therefore, NT may be a viable strategy to remove NO3−-N from the soil, and thus, reduce NO3−-N contamination of groundwater. However, it should be noted that while the use of NT reduces NO3−-N leaching it may come with unintended environmental tradeoffs, including increased NH3 and N2O emissions.  相似文献   

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